Heretofore, porphyrin derivatives have been used as a photoconductive material, an electrophotographic photoreceptor material, an optical memory material, a photocatalyst material, a material for molecular devices, and the like. For example, Patent Literature 1 and 2 disclose porphyrin derivatives containing various substituents at the ring periphery or as axial ligands. Patent Literature 1 and 2 disclose that these derivatives can be used for the aforementioned purposes.
In recent years, porphyrin derivatives have also been used in fluorescent dyes in the field of biochemistry as well as in photosensitizers for photodynamic therapy (PDT) in the field of medicine. Therefore, improving the water solubility thereof has been a challenge. In relation to this, Patent Literature 3 and 4 disclose porphyrin derivatives having improved water solubility.
For example, Patent Literature 3 discloses water-soluble porphyrin derivatives for use in PDT. According to Patent Literature 3, various substituents are introduced to the periphery of the porphyrin ring so as to improve the water solubility (Claim 19, etc., of Patent Literature 3).
Further, Patent Literature 4 discloses an amphipathic metalloporphyrin complex with cationic hydrophilic groups and lipophilic groups introduced to the ring periphery. Patent Literature 4 further discloses that this complex can be used as a pharmaceutical composition.
Heretofore, porphyrin derivatives having water solubility as described above are known. However, such derivatives are synthesized by introducing a cationic or anionic functional group, or a functional group such as hydrophilic macromolecules, to the periphery of the porphyrin ring, making the synthesis of the derivatives difficult. Further, considering use in the field of biochemistry and use in the field of medicine, porphyrin derivatives are required to have both water solubility and lipophilicity (oil solubility). However, synthesizing a porphyrin derivative that satisfies such a requirement is difficult.